From the introduction: Welcome to the world of DOOM, where the UAC megacorporation harvests Hell for energy and demonic invasion is a regular occurence. You will find yourself placed in either Mars or the nearby hellscape, shortly before the BioScience director of the Mars base, Olivia Pierce, is set to begin a final demonic incursion in an attempt to gain demonic divinity. But that's not particularly important. What's important is that there's gonna be a shitload of demons soon, and you're gonna have to deal with that in one way or another. Get to it. You got ten years ahead of you.